Refactoring, Therapeutic Attitude to Programming.
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This document discusses refactoring and common programming diseases. It begins with an introduction to refactoring, defining it as improving the design of existing code without changing its external behavior. It then discusses reasons for refactoring like improving code understandability and design. It also discusses when refactoring should occur, such as when adding new features or fixing bugs. The document then covers common programming diseases called "code smells" including bloated code, object-oriented abuses, redundancies, and couplings. It provides examples and treatments for each smell type.
Refactoring, Therapeutic Attitude to Programming.
- 1. Refactoring Therapeutic Attitude to Programming 12/23/2017 Refactoring 1 Amin Shahnazari University of Isfahan
- 2. uestions 12/23/2017 Refactoring 2 1. What is the most terrible thing to a programmer? 2. What are the common programming diseases?
- 3. 12/23/2017 Refactoring 3 1. What is the most terrible thing to a programmer? - Clean code - Technical debt - Refactoring definition - Why should you refactor? - When Should you refactor? - Learning Refactoring. 2. What are the common programming diseases? - Bloaters - Object Oriented Abuses - Change Obstacles - Redundancies - Couplings Table of Content
- 4. uestions 12/23/2017 Refactoring 4 MOST TERRIBLE What is thing to a programmer? the Question 1:
- 6. NO --Say-- to Evil 12/23/2017 Refactoring 6 Old Wrong Engineering Mentality: If it works, Don’t fix it! Think about tomorrow! Consider Changes!
- 7. 12/23/2017 Refactoring 7 Clean Code • Clean code is obvious for other programmers. All of that makes code sloppy and difficult to grasp should resolve. • Clean code doesn't contain duplication or redundant code. This increases the cognitive load and slows down the progress. • Clean code contains a minimal number of classes and other moving parts. Less code = Less stuff to keep in your head, Less maintenance, Fewer bugs. • Clean code passes all tests. How can we maintain and extend code without the fear that it will stop working? You cannot test dirty code! • Clean code has minimal dependencies! The more dependencies it has, the harder it is to maintain and change it in the future.
- 8. 12/23/2017 Refactoring 8 Technical debt If you get a loan from a bank: • This allows you to make purchases faster. • You pay extra for expediting the process. • If the amount of interest exceeds your total income, making full repayment impossible. The same thing can happen with code: • You can temporarily speed up with dirty code (debt). • This will gradually slow your progress every day. • You have to eventually pay off the debt. • I hope that you can pay off debt successfully.
- 9. 12/23/2017 Refactoring 9 Cause of Technical debt • Business pressure. • Lack of understanding of the consequences of technical debt. • Failing to combat the strict coherence of components. • Lack of tests. • Lack of documentation. • Lack of interaction between team members. • Long-term simultaneous development in several branches. • Lack of compliance monitoring. • Programmer incompetence.
- 10. 12/23/2017 Refactoring 10 Refactoring definition • It is a disciplined way to clean up code that minimizes the chances of introducing bugs. • In essence when you refactor you are improving the design of the code after it has been written. • It’s not about performance optimization. “Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure.” --Martin Fowler--
- 11. 12/23/2017 Refactoring 11 Why should you refactor? • Refactoring Improves the Design of Software. Without refactoring, the design of the program will decay. As people change codes, the code loses its structure. Loss of the structure of code has a cumulative effect. • Refactoring Makes Software Easier to Understand. Think about future developer! Often this future developer is you! Programs that are hard to read are hard to modify. • Refactoring Helps You Find Bugs. Refactoring is rather like tidying up the code. If I refactor code, I work deeply on understanding what the code does. By clarifying the structure, you clarify assumptions you’ve made. • Refactoring Helps You Program Faster. Without a good design you progress quickly for a while, but soon the poor design start to slow you down. You spend more time to find and fix the bugs and changes takes time.
- 12. 12/23/2017 Refactoring 12 When should you refactor? • Refactoring When Add Feature. Helps to understand some code which needs modification. When there is a design that does not help add a feature easily. • Refactoring When You Need to Fix a Bug. Refactor to help improve understanding. • Refactoring As You Do a Code Review. Code review help spread knowledge through a development team. The last chance to tidy up the code before it becomes available to the public. It's best to perform such reviews in a pair with an author.
- 13. 12/23/2017 Refactoring 13 What Do I Tell My Manager? • Quality Driven Manager: It’s not so difficult, implement refactoring in review process. • Schedule Driven Manager: The fastest way is to refactor, therefore I refactor! • Quality-Schedule Manager: Don’t tell!
- 14. 12/23/2017 Refactoring 14 Refactoring, Improve the Design of Existing Code Learning Refactoring Martin Fowler and Et al. https://refactoring.guru Refactoring Guru website
- 15. 12/23/2017 Refactoring 15 Learning Refactoring Martin Fowler 1963 (age 53–54) Kent Beck 1961 (age 55–56)
- 16. uestions 12/23/2017 Refactoring 16 DISEASES? What are the common programming Question 2:
- 17. 12/23/2017 Refactoring 17 Refactoring is a therapeutic attitude to programming diseases! • Just like a medical doctor, you need to cure these diseases. • You need to detect diseases from signs in codes. • A list of common diseases and their treatments already provided. • In refactoring nomenclature, diseases called Code Bad Smells.
- 18. 12/23/2017 Refactoring 18 5 • Bloaters Code, methods and classes that have increased to such huge proportions that they are hard to work with. Class of diseases • Object Oriented Abuses Incomplete or incorrect application of object-oriented programming principles. • Change Obstacles If you need to change something in one place in your code, you have to make many changes in other places too. • Redundancies Some pointless and unneeded codes whose absence would make the code cleaner, more efficient and easier to understand. • Couplings Excessive coupling between classes.
- 19. 12/23/2017 Refactoring 19 Bloaters • Long Methods • Large Classes • Primitive Obsession • Long Parameter List • Data Clumps
- 20. 12/23/2017 Refactoring 20 Long Method Bloaters • A method contains too many lines of code. • Generally, any method longer than ten lines should make you start asking questions. • If you feel need to comment something in a method, write a method instead. Signs Reason Treatment • Since it is easier to write code than to read it, this "smell" remains unnoticed until the method turns into an ugly. • Extract Method, Replace Temp with Query, Introduce Parameter Object. • Preserve Whole Object, Replace Method with Method Object. • Decompose Conditional.
- 21. 12/23/2017 Refactoring 21 Large Class Bloaters • A class contains many fields/methods/lines of code.Signs Reason Treatment • Programmers usually find it mentally less taxing to place a new feature in an existing class than to create a new class for the feature. • Class has several responsibilities. • Extract Class • Extract Subclass • Extract Interface • Duplicate Observed Data
- 22. 12/23/2017 Refactoring 22 Primitive Obsession Bloaters • Use of primitives instead of small objects for simple tasks. • Use of constants for coding information. • Use of string constants as field names for use in data arrays. Signs Reason Treatment • "Just a field for storing some data!" the programmer said. • Creating a primitive field is so much easier than making a whole new class, • Replace Data Value with Object. • Introduce Parameter Object, Preserve Whole Object. • Replace Type Code with Class, Replace Type Code with Subclasses or Replace Type Code with State/Strategy. • Replace Array with Object.
- 23. 12/23/2017 Refactoring 23 Long Parameter List Bloaters • More than three or four parameters for a method.Signs Reason Treatment • A long list of parameters might happen after several types of algorithms are merged in a single method. • Replace Parameter with Method Call. • Preserve Whole Object. • Introduce Parameter Object.
- 24. 12/23/2017 Refactoring 24 Bloaters • Sometimes different parts of the code contain identical groups of variables. Signs Reason Treatment • Often these data groups are due to poor program structure or "copy-paste programming”. • Just delete one of the data values and see whether the other values still make sense. If this is not the case, this is a good sign that this group of variables should be combined into an object. • Extract Class • Introduce Parameter Object • Preserve Whole Object Data Clumps
- 25. 12/23/2017 Refactoring 25 OO Abuses • Switch Statements • Temporary Field • Refused Bequest • Alternative Classes with Different Interfaces
- 26. 12/23/2017 Refactoring 26 OOAbuses • You have a complex switch operator or sequence of if statements. Signs Reason Treatment • Often code for a single switch can be scattered in different places in the program. When a new condition is added, you have to find all the switch code and modify it. • when you see switch you should think of polymorphism. • Extract Method, Move Method. • Replace Type Code with Subclasses • Replace Type Code with State/Strategy. • Replace Conditional with Polymorphism. • Replace Parameter with Explicit Methods. • Introduce Null Object. Switch Statements
- 27. 12/23/2017 Refactoring 27 OOAbuses • Temporary fields get their values only under certain circumstances. Outside of these circumstances, they are empty. Signs Reason Treatment • Oftentimes, temporary fields are created for use in an algorithm that requires a large amount of inputs. • These fields are used only in the algorithm and go unused the rest of the time. • Extract Class. • Replace Method with Method Object. • Introduce Null Object Temporary Field
- 28. 12/23/2017 Refactoring 28 OOAbuses • If a subclass uses only some of the methods and properties inherited from its parents, the hierarchy is off-kilter. Signs Reason Treatment • Someone was motivated to create inheritance between classes only by the desire to reuse the code in a superclass. But the superclass and subclass are completely different. • Replace Inheritance with Delegation. • Extract Superclass Refused Bequest
- 29. 12/23/2017 Refactoring 29 OOAbuses • Two classes perform identical functions but have different method names. Signs Reason Treatment • The programmer who created one of the classes probably didn't know that a functionally equivalent class already existed. • Rename Method • Move Method, Add Parameter • Parameterize Method. • Extract Superclass. Alternative Classes with Different Interfaces
- 30. 12/23/2017 Refactoring 30 Change Obstacles • Divergent Change • Shotgun Surgery • Parallel Inheritance Hierarchies
- 31. 12/23/2017 Refactoring 31 ChangeObst • You find yourself having to change many unrelated methods when you make changes to a class. Signs Reason Treatment • Often these divergent modifications are due to poor program structure or "copy-paste programming”. • Extract Class. • Extract Superclass • Extract Subclass Divergent Change
- 32. 12/23/2017 Refactoring 32 ChangeObst • Making any modifications requires that you make many small changes to many different classes. Signs Reason Treatment • A single responsibility has been split up among a large number of classes. • Move Method • Move Field • Inline Class Shotgun Surgery
- 33. 12/23/2017 Refactoring 33 ChangeObst • Whenever you create a subclass for a class, you find yourself needing to create a subclass for another class. Signs Reason Treatment • All was well as long as the hierarchy stayed small. But with new classes being added, making changes has become harder and harder. • Move Method • Move Field. Parallel Inheritance Hierarchies
- 34. 12/23/2017 Refactoring 34 Redundancies • Comments • Data Class • Lazy Class • Duplicate Code • Dead Code • Speculative Generality
- 35. 12/23/2017 Refactoring 35 Redundancies • A method is filled with explanatory comments.Signs Reason Treatment • If you feel that a code fragment cannot be understood without comments, try to change the code structure in a way that makes comments unnecessary. • The best comment is a good name for a method or class. • Extract Variable. • Extract Method. • Rename Method • Introduce Assertion. Comments
- 36. 12/23/2017 Refactoring 36 Redundancies • Two code fragments look almost identical.Signs Reason Treatment • Duplication usually occurs when multiple programmers are working on different parts of the same program at the same time. • Extract Method, Pull Up Field • Pull Up Constructor Body. • Form Template Method. • Substitute Algorithm • Extract Superclass, Extract Class • Consolidate Conditional Expression • Consolidate Duplicate Conditional Fragments. Duplicate Code
- 37. 12/23/2017 Refactoring 37 Redundancies • So if a class doesn't do enough to earn your attention, it should be deleted. Signs Reason Treatment • Perhaps a class was designed to be fully functional but after some of the refactoring it has become small. • Inline Class • Collapse Hierarchy Lazy Class
- 38. 12/23/2017 Refactoring 38 Redundancies • A data class refers to a class that contains only fields and crude methods for accessing them (getters and setters). Signs Reason Treatment • But the true power of objects is that they can contain behavior types or operations on their data. • Encapsulate Field • Encapsulate Collection • Move Method, Extract Method • Remove Setting Method, Hide Method Data Class
- 39. 12/23/2017 Refactoring 39 Redundancies • A variable, parameter, field, method or class is no longer used. Signs Reason Treatment • When requirements for the software have changed or corrections have been made, nobody had time to clean up the old code. • Using IDE. • Inline Class, Collapse Hierarchy • Remove Parameter Dead Code
- 40. 12/23/2017 Refactoring 40 Redundancies • There is an unused class, method, field or parameter.Signs Reason Treatment • Sometimes code is created "just in case" to support anticipated future features that never get implemented. • Collapse Hierarchy. • Inline Class. • Inline Method • Remove Parameter. Speculative Generality
- 41. 12/23/2017 Refactoring 41 Couplings • Feature Envy • Incomplete Library Class • Middle Man • Inappropriate Intimacy • Message Chains
- 42. 12/23/2017 Refactoring 42 Couplings • A method accesses the data of another object more than its own data. Signs Reason Treatment • This smell may occur after fields are moved to a data class. If this is the case, you may want to move the operations on data to this class as well. • Move Method • Extract Method Feature Envy
- 43. 12/23/2017 Refactoring 43 • One class uses the internal fields and methods of another class. Signs Reason Treatment • Keep a close eye on classes that spend too much time together. • Good classes should know as little about each other as possible. • Move Method, Move Field • Extract Class, Hide Delegate • Change Bidirectional Association to Unidirectional. • Replace Delegation with Inheritance. Inappropriate Intimacy Couplings
- 44. 12/23/2017 Refactoring 44 • In code you see a series of calls resembling $a->b()->c()->d()Signs Reason Treatment • A message chain occurs when a client requests another object, that object requests yet another one, and so on. • These chains mean that the client is dependent on navigation along the class structure • Hide Delegate. • Extract Method • Move Method. Message Chains Couplings
- 45. 12/23/2017 Refactoring 45 • If a class performs only one action, delegating work to another class, why does it exist at all? Signs Reason Treatment • In other cases, it can be the result of the useful work of a class being gradually moved to other classes. • The class remains as an empty shell that does not do anything other than delegate. • Remove Middle Man Middle Man Couplings
- 46. 12/23/2017 Refactoring 46 Thanks For your attentions